The invention relates generally to the field of marine geophysical surveying. More particularly, at least in some embodiments, the invention relates to methods for determining geodetic locations of positions on streamers towed at water depths which make impractical the use of geodetic position sensor signals and tail buoys.
Marine geophysical surveying techniques known in the art include seismic surveying and electromagnetic surveying. In such surveying techniques, a survey vessel or other vessel may tow one or more streamers. A streamer is essentially a long cable with sensors disposed at spaced apart locations along the length of the cable. Seismic streamers may include pressure responsive sensors, particle motion responsive sensors, or combinations and variations thereof generally responsive to seismic energy propagating in a body of water. Electromagnetic sensors may include, without limitation, electrodes, wire coils, magnetometers, or other devices to detect electromagnetic fields in the body of water. Such fields may be naturally occurring or may be induced by actuating an electromagnetic energy source in the water.
The foregoing surveys may be used to generate images of the distribution of acoustic and electrical properties of formations below the water bottom. Such images may be used to predict the location of hydrocarbons or other useful fluids prior to or in conjunction with drilling operations. Generating accurate images requires, among other things, accurate location of each of the sensors on each of the streamers at all times during survey operations.
In some cases, marine geophysical surveying may be performed using only one geophysical sensor streamer towed near the water surface. Another streamer may be towed at a selected depth in the water wherein the other streamer is completely submerged. It is desirable to have a method that can enable determining geodetic position along an entire submerged geophysical sensor streamer from information from only two geophysical sensor streamers.